Pump-gear type with unloading



. J. A. LAUCK PUMP-GEAR TYPE WITH UNLGADING April 2s, 195oy Filed sept. 18. 1947 7 Sheets-Sheet l J. A. LAUCK PUMP-GEAR TYPE WITH UNLOADING April 25, 195.0

Filed sept. 18, 1947 7 Sheets-Sheet 2 ww SQ April 25, 1950 J. A. I AucK PUMP-GEAR TYPE WITH uNLoADmc 7 Sheets-Sheet' 4 Filed sept 18. 1947 ,7 Sheets-Sheet 5 J..- A. LAUcK Pun-GEAR TYPE wrm UNLOADING y April 25, 1950'4 F'1`1edsep-z. 1e. l194'? 00000 00,. 00 kwas April 25, 1950 J. A. L AucK PUIPGEAR TYPE WITH UNLOADING 7 Sheets-Sheet 6 Filed Sept. 18, 1947 April 25, 195o J. A. LAUCK 2,505,191

PUMP-GEAR TYPE WITH UNLOADING Filed Sept. 18, 1947 7 Sheets-Sheet 7 Patented Apr. 25, 195i) 2,505,191 PUMP- GEAR TYPE wrrn UNLoAmNG John A. Lauck, South Euclid, Ohio, assignor to Borg-Warner Corporation, Chicago, lll., a corporation of Illinois Application September 18, 1947, Serial No. 774,720

13 Claims. (Cl. 103-11) This invention relates to hydraulic power units, and particularly to an arrangement of xed dis placement intermeshing gear type pressure generators or pumps wherein both generators operate to deliver noncompressible liquid pressure to a resistance consumer such as a piston motor during a rst stage of operation, and wherein automatic means function to cut out one of said generators during a second stage of operation.

The problem of effectivelyunloading a selected one of the working liquid pressure generators of a group upon the occurrence of a predetermined maximum delivery pressure, has long existed without a Asatisfactory solution. vThe principal objection to proposals heretofore tried, has been the necessity of employing largel complicated valve structures for unloading the entire output volume f one of the generators or pu'mps and returning this discharge liquid to a zone of low pressure. These valves have been further unsatisfactory because of the expense of manufacseal with the gear side faces, these bushings lbeing held in pumping seal relation by means of the pressure generated by the corresponding gears and there being further provided pressure sensitive pilot control valve means, responsive to the development of a predetermined value of com-v bined output pressure for relieving the pressure,

. maximum value of combined output pressure for ture and maintenance thereof. An additional limitation of prior proposals resides in their ineffectiveness to maintain a definite and dependable range of pressures, during which the pumps are loaded and a clear cut and definite pressure point at which the selected one of .the pumps is unloaded and maintained unloaded without the presence of hunting or inadvertently cutting in and out of said selected one of said pumps.

It is, therefore, a general object of the present invention to provide a working pressure liquid generating unit including a plurality of intermeshing gear pumps, for effectively loading one or more of said pumps during a rst selected range of pressures and for effectively unloading at least one of said pumps and dependably maintaining the salme unloaded under other selected conditions of operation. l

- It is an object of this invention to provide in a power 'unit of -the above character a novel `arrangement making it practicable to employ fixed displacement intermeshing gears as the working liquid pressure generating means with the further provision of a novel and effective pilot control valve means for causing the `pressure load to be relieved from at least one of 4said generators under predetermined conditions of operation.

It is a more particular object to provide a liquid pressure power-generating unit comprising a pair of intermeshing gear type pumps, Vat least f one of said pumps having axially adjustable end l i Y plates or bushing means for'providlng a pumping relieving the fluid pressure acting in said selected pump on the back side of said end bushing seal [in4 the direction of pumping seal engagement,

said pilot valve being particularly characterized by the inclusion of means isolating the same from any effect thereon by the action of the pressure fluid relieved thereby.

It is a further object of this invention to incorporate in a novel manner in a unitary housing assembly, a plurality of pairs of intermeshing gears forming separate liquid pressure generators, each having pressure loadable end bushings or bearings responsive to the pressure generated by the respective pumps eiective under predetermined conditions to maintain said bushings in pumping seal engagement with the corresponding side faces of the gears, the arrangement being further particularly characterized by the incorporation in said housing of pilot control valve means responsive to the combined or joint output pressure of said pumps when the same reaches a selected maximum value to relieve the loading pressure acting on said bushings of one of said pumps and thus permit the corresponding bushings to move axially out of pumping seal engagement with the adjacent gear side faces, the arrangement being still further particularly characterized by the provision of means rendering said pilot control Valve means non- 4responsive to the pressure fluid acting to load` y said bushings.

It is a still further particular object to provide an arrangement of the above character wherein the pressure liquid from the pump that remains in operation is effective to maintain the pilot control valve open until it is desired to reload the unloaded pump, thus assuring the desired condition of operation.

It is an alternative object to provide an arrangement of the above general character wherein the pump that is caused to remain in operation, functions to deliver working pressure to a. consuming motor for the purpose of providing a high pressure low volume following a rst relatively large volume low pressure slack take-up stage of operation.

Other and more particular objects, advantages and uses of the present invention will become apparent from a reading of the following specification taken in connection with the appendeddrawings forming a part thereof and wherein:

Fig. 1 is a side elevational view of a unitary pump assembly incorporating a preferred embodiment of the present invention;

Fig. 2 is a cross sectional view taken substantially on the line 2-2 of Fig. l, bringing out to advantage the side by side relationship of the separate gear type high pressure working liquid generators connected together in driving relationship;

Fig. 3 is a cross sectional view taken substantially on the line 3-3 of Fig. 2, and further bringing out to advantage the relationship of the two liquid pressure generators and the oneway check valve located therebetween for preventing reverse flow following the unloading of one of the gear units;

Fig. 4 is a cross sectional view taken substantially on the line 4--4 of Fig. 2, and showing the stationary end plates or bushings as well as bringing out to advantage the arrangement of the pilot control valve rendering the same solely responsive to the joint output pressure generated Iby the units while completely isolating or balancing the same against the influence of the loading pressure acting on the pumping seal denlng bearing bushings;

Fig. 5 is a cross sectional view taken substantially on the line 5 5 of Fig. 2, bringing out to advantage the form and arrangement of the pressure loadable end plates or bushings functioning to engage the gear side faces and which are radially coextensive with the gear teeth, and define a pumping seal with the gear side faces when pressure loaded and function to break the pumping seal when unloaded;

Fig. 6 is a cross sectional view taken substantially on the line 6-6 of Fig. 2 showing the pumping seal defining bushings on the pressure loaded side of the smaller displacement intermeshing gear generator or pump bringing out to advantage the relief valve arrangement;

Fig. '7 is a schematic view bringing out in a more illuminating manner the arrangement of the parts making up the preferred embodiment of the present power unit and the modeof coaction under operating conditions;

Fig. 8 presents curves showing the relationship of pressure and piston travel believed to bring out even more effectively the actual conditions of operation shown in Fig. 7;

Fig. 9 is a schematic view of an alternative embodiment of the present invention bringing out the relationship of parts and mode of coaction and in which embodiment both pressure generators function during a. rst slack take-up stage of operation to deliver a relatively large volume of pressure liquid at a relatively low pressure followed by the unloading of the larger one of the generators and the continued delivery of' pressure liquid by the smaller generator at high pressure but relatively small volume;

Fig. l0 presents curves showing the relationship of pressure and piston travel believed to bring out even more effectively the actual conditions of operation shown in Fig. 9;

Fig. l1 is a schematic view of another alternative embodiment incorporating a simplified arrangement of pilot control valve; and

Fig. l2 is a schematic view vof still another alternative embodiment showing a piston type of pressure generator as the second or relatively small displacement pump.

Referring in greater detail to the figures of the drawing and first to the preferred embodiment of Figs. 1 through 7, there is shown a liquid pressure power generator indicated generally at I0, comprising a unitary housing il, having a common low pressure liquid inlet l2, a common high pressure outlet I3 and incorporating therein a first intermeshing gear type pressure generator or pump P-I, a second intermeshing gear type pressure generator or pump P-2, a oneway check valve assembly I6, a relief valve assembly R-I and a pilot control valve assembly C-I.

The particular problem solved by this embodiment is the furnishing of a range of liquid pressures to a resistance type of pressure consumer or motor such as the piston motor M--I indicated schematically in Fig. 7 wherein it is of critical importance to deliver a range of pressures up to a selected maximum value followed by the automatic unloading of the first or primary large displacement pressure generator or pump P-i, while assuring the maintenance of this condition as long as desired. It is important to provide an effective and commercially practicable arrangement for relieving the load or back pressure against which generator P--i must act, following the delivery of a predetermined maximum value of pressure uid to motor M-l, as well as to provide an effective and commercially practicable arrangement for assuring that generator P-l remains in an unloaded condition and does not hunt or become inadvertently or prematurely reloaded. The choice of the particular construction of pump or generator P--I in combination with the particular construction and arrangement of pilot control valve C-I and secondary energizing pump P-Z comprises the particular subject matter to which this preferred embodiment is directed.

Pump or liquid pressure generator P-i is preferably constructed in general conformity with the disclosure and claims of earlier Roth and Lauck Patent No. 2,420,622, comprising essentially a pair of intermeshing gears il, i8 reyceived in pump chamber I9 within housing Il and having stationary bearing bushing and seal assemblies 2li engaging the gear faces on one side thereof in pumping seal relation and axially adjustable bearing bushing and seal assemblies 2| engaging the gear side faces on the opposite side therefrom bushings 20, the bushing assemblies 2| being arranged to be pressure loaded by means of liquid pressure generated by the gears and controlled in a special manner that will be pointed out. The bushings comprise flange portions 20a and Zia, formed radially coextensive with the gear teeth. the inner terminal portions of the flanges presenting faces 20b, 2lb in pumping seal relation with the gear side faces. The radial ixmer extremities of faces 20h and 2lb communicate with annular relief recesses 20c, Zic, these respective relief recesses being placed in communication with the low pressure inlet through axially extending channels 23d, 2id, leading to the pump inlet as will appear. The relief recesses c and l2|c control the effective area of faces 20o and 2lb and hence the axial forces tending to produce relative axialv movement between the bushing flanges and the gear o relief .of pressure fluid by the functioning of pilot control valve C-,I as will appear. Motive surfaces 2te together with the associated tubular extension 2U and the opposed housing wall form a motive pressure chamber M into which is delivered liquid pressure generated by pump P--|, this liquidv pressure being directed from the discharge side of the teeth of gears I1 and I3 axially along the periphery of bushing flanges 2|a at their point of convergence, this passage being designated 22v (Fig. 5). The convering peripheries of bushing flanges 2|a at the opposed extremity of mating surface 23 from passage 22 Q would normally likewise form with the housing va passage similar to passage 22 but this is prevented by the drilling of an axially extending bore and inserting therein 'a closure plug 24 thus preventing the recirculation of pressure fluid back to the inlet side of the 'gear teeth. Seal rings 2|g provide the requisite seal. To provide therequisite lubrication, complementary recesses 23,

to close the bore and assist in preventing the extrusion of the flexible seal ringo29 when under pressure. The result of this arrangement is an increased effective pressure responsive area 33d on the back face of the bushing flange as differentiated from the usual arrangement wherein the flexible seal 29 is received in a two-sided channel formed in the housing bore, as in the case of pump P-I. by pump P--2 is likewise directed from the discharge side of the teeth ofA gears 3|, 32 axially along the periphery of the bushing flanges 33 at their position of convergence with housing Il, this passage being designated 34 in Fig. 6. Pump P--2 is connected in continuous driving relationship with pump P-I through journal connector 32a on the terminal of journal 32h and cooperating journal |3a of gear I3, both pumps being arranged to be driven through journal |3b having terminal connector |3c. Coil compression springs' 33 function to maintain bushing flanges 33 in initial pumping seal relation with the side faces of gears 3| and 32.

` One-way check valve I6 interposed between 26 are provided in ,the faces 2lb, these recesses communicating with annular groovesv 25a and 26a extending substantially but not all 4the way around the faces 2lb/and functioning to communicate lubricant thereabout thus preventing undue wear which might otherwise occur because of the axial movement ofthe bushings into and out of sealing engagement with the gear side ment functioning to prevent gear I1 from moving axially away from flange 20a when the opposite bushing flange 2|a is unloaded or has the pressure relieved therefrom bythe operation of pilot` 5 control valve C-I. A

The secondary or energizing `pump P-2 is lconstructed in a manner similar to that of pump P--I, hence, no detailed description thereof is deemed necessary. It will be noted that due to the contemplated small displacement of pump lP---2 a different construction of bearing and housing relationship is employed in order to provide the maximum motive surfacel area on the back face of the bushing flange, this particular construction being disclosedl and claimedin Wichorek application, Serial Number 687,379,

' filed July 3'1, 1946, Patent No;` 2,472,031. Essentially a straight bore 23 receives a ring seal 23 and the bushing is provided with a step 30 functioning effective to open valve |6a and permit flow from pump P-i to the commonv'outlet |3 while any tendency for liquid to flow from pump P--2 in the direction of the discharge side of pump P-| is pevented by the automatic closing of check valve Relief valve R-I (see Fig. 6) comprises a disc or conical shaped valve proper 36 urged in the direction of its seat against -the combined pressure from pumps P-I and P-2 by means of a coll compression spring 31. The value of the 'compression of spring 31 is chosen with reference to` the maximum pressure to which motor M-I is to be subjected and may, for example, be given a value such as to provide for the delivery of a pressure of the order of 50 p. s. i. above the value of the pressure for which pilot control valve C| is set to operate to unload pump'P-I. Valve proper 36 has a rearwardly extending stem 36a terminating in a guide 36h provided with a limited axially extending clearance passage 36e permitting a limited jrate of now of liquid into communication with pilot control valve assembly C-I as will appear. Closure member 31a has a threaded cooperation with housing to provide for adjusting the compression value of spring 31 and hence the value of delivery pressure at which i prises a disc or conical shaped valve proper 33 urged in the direction oi' its seat by means of coil compression spring 33 against the flow of liquid pressure from communication with the back motive surface 2|e of bushing flange 2|a, this comsmunication being effected through passage Ila in housing I. Stem 33a connects valve proper 33 with motive piston 43. the surface 40a of which piston is responsive to the combined discharge pressures of pumps P-I and P-2 to cause open- The pressure generated lng of valve 38 upon this pressure reaching a predetermined maximum value. to thus relieve the pressure uid acting on motive surface 2 le of the bushing flanges 2|a and unload pump P--I.

It is important to note that the area 40h of piston 40 is the same as the effective area 38h of valve 38 thus completely balancing valve 38 against any influence exerted by the pressure fluid from passage lla. In other words. the development of pressure in communication with motive surface 2|e on the back side of bushing ianges 2 la, while in communication through passage Ila with valve 38, nevertheless, has no influence upon valve 38. This valve 38 is completely and entirely responsive to the delivery pressure beyond check valve IE, which is the delivery pressure of both pumps P-l and P2 when operating or the pressure of pump P2 when pump P-I has been unloaded. This is of particular importance in connection with maintaining pump P-I unloaded following the unloading operation of pilot control valve C-I. Pump P2, while of a, very small displacement, such for example, as of the order of .05 cubic inch, is of sufdcient capacity to make up for any losses by leakage, etc., and at the same time maintain the requisite pressure on motive surface 40a oi piston 40 for the purpose of maintaining valve 38 open. Closure member M has a threaded relationship with housing Il for the purpose of adjusting the compression value of spring 39. The valve 38 and piston are preferably mounted in a separate closure member 42 which facilitates manufacture. When it is desired to'eifect the reversal of motor M-I valve 4l (Fig. '7) will be operated whereupon pressure will be relieved from the rst side of motor Ml and delivered to the opposite side thereof, pilot control valve 38 will close due to the relaxation of pressure acting cn motive piston surface 40d, following which the pressure in bushing motive chamber M will be built up to effect the requisite pumping seal in pump P-l, thus reloading pump P-I.

Valve 45 (Fig. 2) is urged in the direction of its seat by coil compression springs 45a and functions to maintain a small differential of pressure between the inside of the pump in the area of the bushing terminals and the pump inlet, which may be of the order of 10 to 15 p. s. i. and is important at high altitudes in preventing the drawing of too high a vacuum.

The operation of the embodiment shown in Figs. 1 through 'l will now be apparent particularly by reference to Figs. '7 and 8. Upon starting pumps P-l and P2 it will be seen from Fig. 8 that the common discharge pressure will be built up in general conformity with the dotted line curve showing the relationship between pressure and piston travel, the exact shape of this curve being determined, of course, by the character of the resistance to movement offered by the load on motor M-L The solid line curve in Fig. 8 is intended to indicate the mean relationship between the pressure and the piston travel. It will be noted that in the example selected the pressure acting on ymotor M-I will be built up to about 1500 p. s. i. following which this value of pressure becomes effective on motive surface 40a of piston 40 to open valve 38 and discharge or relieve the pressure fluid from rear motive surface Zie of bushing flanges 2in, thus allowing the bushing anges to move out of pumping seal contact with the side faces of the gears and unload the pump P-L After this numbing seal is broken in pump P-I there will be no further delivery from this pump past check valve i6. the liquid in the pump merely recirculating as the gear teeth continue to be rotated. Pump P2 will continue to function as an energizing or make-up pump delivering pressure fluid to maintain piston 40 in operated position and make up for any loss of fluid due to leakage, there being no further movement of motor M-i. This is assured by the fact that relief valve R-l is set to operate at a pressure of only 50 p. s. i. above that for which pilot control valve C-I operates. namely, at 1,550 p. s. i. This small dii'- ferential of pressure is insufficient to produce any appreciable movement of motor M-I against the normal resistance to its movement existing under these circumstances. The very small displacement of pump P2 is insuficient to produce any practical rate of movement of motor M-I even were relief valve R-l set for a higher differential than 50 p. s. i.

Turning now to the alternative embodiment of the present invention disclosed in Figs. 9 and 10, it will be seen that the arrangement of structure is similar to that of Figs. 1 through 7 except for the choice of relative displacements of pumps P--I and P-3 as well as the choice of operating pressures for pilot control valve C-Z and relief valve Rf-, these differences being explained bythe difference in the work cycle for which the liquid pressure power generator of Fig. 9 is provided. Essentially motor M2 is required to be operated through a first slack take-up stage S-I requiring a relatively large rate of flow to the motor at low pressure followed by a working stage S-2 during which only a small volume of pressure liquid is required to be delivered to the motor M-2 but this small volume must be delivered at a relatively high pressure. Upon starting pumps P-l, P-3 the pressure, piston travel relationship followsgenerally the pattern indicated by the dotted line curve of Fig. 10. In the example assumed the combined output pressure will rise to a value in the neighborhood of 300 p. s. i., suilcient to move the motor M-2 through the slack take-up stage S-I and upon the engagement of the work and the initiation of the work stage S-Z the combined pressure of pumps P-I and P-3 becomes effective in acting upon the piston of pilot control valve C2 to open the pilot control valve and cause the unloading of the pump bushing from pumping seal contact with the associated gear side face in the manner described in connection with Fig. 7. Continued operation of pump P-3 is effective to deliver pressure fluid to motor M-2 during the working stage S- 2, this pressure sion values of the springs in relief valve Rf-2 acteristics.

In Fig. 11 there is disclosed schematically a somewhat simplified embodiment combining the relief valve and the pilot control valve in one unit indicated generally at RIJ-3. Valve proper 50 is arranged tobe operated by motive piston 50a exposed Ato the common discharge pressure and functioning to cooperate with the inlet terminal of conduit IIb in a manner such that the movement of piston Illa first operates valve proper 50 to effect the unloading of the bushing. associated with the pump P-l.

The developthe terminal surface of said flange engaging with the adjacent gear side face in pumping seal relation, said bushing means including a pressure 4 responsive surface opposed to said terminal surment of a value of pressure by pump P-2 in excess ofthe selected differential, determined by spring 50c, becomes effective to move piston Illa still further uncovering the inlet port vto conduit 50h and relieve this excess pressure through conduit 50h to the low pressure side of the pumps.

It will thus be seen that a simplified combination of relief valve and pilot control valve has been provided for certain less exacting installations.

In Fig. 12 there is shown schematically still another alternative modification differing from the above forms in the substitution of a piston type energizing pump P-4 for the previously employed gear type second pumps P-2 and P-3. This pump P-4 comprises a reciprocal piston 55 actuated by an eccentric 58 rotated with pump P-f-i. A one-way-check valve B1 cooperates with the intake and discharge stroke oi' piston 55 providing for delivery of pressure from pump P-4 on the outward stroke and preventing reverse flow on the intake stroke thereof. This piston form of pump P-l is important in installations where it is critical to have an inexpensive energizing pump of extremely small displacement of the order of .01 to .02 cubic inch for example. the gear type pump being impracticable for such small capacities.

While the specific form of pressure loading of the pumps disclosed and claimed in earlier Roth and Lauck Patent No. 2,420,622 is herein em ployed because of the unusual advantages ac- .cruing therefrom, itwillbe understood that other known forms of pressure loading may be incorporated and are contemplated as coming withinthe broader scope of the present invention.

While the present invention has been disclosed in connection with certain specific embodiments thereof it is to be understood that these are by way of example rather than limitation and that the present invention is deivlned'by the appended claims which should be given a scope consistent with the prior art.

What is claimed is:

l. In a liquid pressure, power generating unit, means defining a first fixed displacement intermeshing gear type pump; means deflninga second fixed displacement intermeshing gear type pump; said pumps having a common inlet and delivering to a common outlet; a one-way check valve interposed between the outlet sides of said rstand second pumps effective to prevent flow from said second pump to said first pump; and means responsive to the generation of a combined delivery pressure of a predetermined maximum value effectiveto cause unloading of said first pump while maintaining said second pump in voperation delivering pressure liquid.

2. In a liquid pressure generating power unit, means defining an lenclosing housing having a first pump chamber receiving a rst pair of intermeshing gears, end plate bushingfandbearing defining means normally received in pumping seal engagement with the side faces of said gears, said bushings each ,including a flange radially outwardly coextensive with the adjacent gear teeth,

face and spaced from the adjacent housing wall forming with said housing a, motive pressure chamber, means delivering liquid pressure generated by the corresponding gears to said pressure chamber for normally urging said bushing means into pumping seal engagement with the corresponding gear side face; a second pump chamber in said housing receiving a second pair of intermeshing gears, said housing having a common inlet'to said pairs of gears and a common outlet therefrom, a one-way check valve in said housing interposed between said pairs of gears effective to prevent reverse flow from said second pair of gears to said first pair of gears; means defining a pilot control valve assembly effective upon the occurrence of a combined discharge pressure of a selected maximum value to relieve said pressure fluid from said pressure chamber and permit said bushing means to move axially out of sealing contact with the associated gears and hence unload said first pair of gears, while said second pair of gears continue to deliver liquid pressure to said common outlet.

3. In a liquid pressure generating power unit, means dening an enclosing housing having a first pump chamber receiving a first pair of intermeshing gears, end plate bushing and bearing s seal defining means normally received in pumping seal engagement with the side faces of said gears, said bushings eachincluding a flange radially outwardly coextensive with the adjacent gear teeth, the terminal surface of said flange engaging with the adjacent gear side face in pumping seal relation, said bushing means including a pressure responsive surface opposed to said terminal surface'and spaced from the adjacent housing wall forming with said housing a motive -pressure chamber, means deliveringl liquid pressure generated by the corresponding gears to said pressure chamber for normally urging said bushing means into pumping seal engagement with the corresponding gear side face; a second pump chamber in said housing receiving a second pair oi' intermeshing gears; said housing having a common inlet to said pairs of gears and a common outlet therefrom, a one-way check valve in said housing interposed between said pairs of gears effective to prevent reverse flow from said second pair of gears to said first pair of gears; means defining a pilot control valve assembly effective upon the occurrence of a combined discharge pressure of a selected maximum value to relieve said pressure fluid from said pressure chamber and permit said bushing means to move axially out of sealing contact with the associated gears and hence unload said first pair of gears, while said second pair of gears continue to deliver liquid pressure to said common outlet, said pilot control valve assembly including means responsive to continue delivery by said second pump ber therein, a rst pair of intermeshing gears contained in said first chamber and a second pair of, intermeshing pump gears contained in said second chamber, means connecting said gears in a continuous driving relation, a common liquid inlet to both said pairs of gears and a common outlet in communication with-the discharge sides of said pairs of gears; said housing incorporating a one-way check valve interposed between the discharge sides of said pairs of gears effective to prevent now from said second pair of gears to said first pair of gears; said housing containing means responsive to the generation of a combined delivery pressure of a predetermined maximum value effective to cause unloading of said first pair of gears while maintaining said second pair of gears in operation delivering pressure liquid to said outlet.

5. In a liquid pressure generating power unit, means defining an enclosing housing having a first pump chamber receiving a first pair of intermeshing gears, end plate bushing and bearing defining means normally received in pumping seal engagement with the side faces of said gears, said bushings each including a fiange radially outwardly coextensive with the adjacent gear teeth, the terminal surface of said flange engaging with the adjacent gear side face in pumping seal relation, said bushing means including a pressure responsive surface opposed to said terlminal surface and spaced from the adjacent housing wall forming with said housing a motive pressure chamber, means delivering liquid pressure generated by the corresponding gears to said pressure chamber for normally urging said bushing means into pumping seal engagement with the corresponding gear side face; a second pump chamber in said housing receiving a second pair of intermeshing gears, said housing having a common inlet to said pairs of gears anda common outlet therefrom, a one-way check valve in said housing interposed between said pairs of gears effective to prevent reverse flow from said second pair of gears to said first pair of gears; means defining a pilot control valve assembly effective upon the occurrence of a combined discharge pressure of a selected maximum value to relieve said pressure fluid from said pressure chamber and permit said bushing means to move axially out of' sealing contact with the associated gears and hence unload said first pair of gears, said pilot control valve assembly including means defining a pressure responsive motive surface and a pair of pressure balanced surfaces, means sealing said pair of balanced surfaces from communication with said first valve motive surface, means placing said valve motive surface in communication with the combined output pressure of said two pairs of gears beyond said check valve, and means placing said pressure in said pressure chamber in communication with said balanced surfaces of said valve, whereby said pilot valve is moved to open position in response to a selected maximum value of combined output pressure acting on said valve motive surface and is for relieving the pressure in said pressure chamber uninfluenced by the pressure liquid acting in said pressure chamber.

6. In a'high pressure noncompressible liquid power generating unit comprising means delining a housing having a low pressure liquid inlet, a high pressure liquid outlet and a pair of pump chambers therein; means defining a rst pair of fixed displacement intermeshing gear units in a first one of said chambers; means defining a second pair of relatively small fixed displacement intermeshing gears in a second one of' said chambers, end plate bearing and pumping seal dening means adjacent one side face of said gears in each of said chambers, each of said end plate means having a first surface radially outwardly coextensive with the adjacent gear teeth and engageable with the gear side face ln bearing and pumping seal relation, said end plate means having a second opposed surface responsive to liquid pressure generated by the corresponding gears effective to hold said end plate means in pumping seal relation with the corresponding gear side faces; a one-way check valve in said housing interposed between the outlet side of the gear teeth of said first pump and the outlet side of the gear teeth of said second pump for preventing reverse iiow from said second pump to said first pump; means connecting said pumps in continuous driving relation; pilot control valve means in communication with the pressure acting on the rear surface of the bushing means of one of said gear units for relieving said loading pressure, said pilot control valve including a pressure responsive motive surface and means placing said motive surface of said pilot valve in communication with the joint output pressures of said two pumps whereby the occurrence of an output pressure of a selected predetermined value becomes effective to operate said pilot valve relieving the loading pressure on said first-named pump and permitting the corresponding end plate means to move out of pumping seal engagement with the gear side faces thus unloading said first pump, said second pump continuing to deliver liquid pressure to said outlet and to said pilot control valve effective to maintain said pilot control valve open and thus preventing said end plate of said first pump from prematurely reengaging to reload said first pump.

7. In a high pressure liquid power generating unit comprising means defining a housing having a low pressure liquid inlet, a high pressure liquid outlet anda pair of separate pump chambers therein; a first pair of fixed displacement intermeshing gears in a first one of said chambers; a second pair of relatively small fixed displacement intermeshing gears in the second one of said chambers, means connecting said pairs of gears in continuous driving relation, an end plate in said first pump chamber having a backface normally spaced from the adjacent end wall of said corresponding pump chamber and having portions cooperable with said housing to provide a pressure chamber, said end plate also having a front terminal face subject to the pressures in communication with the corresponding gear teeth and cooperable with the adjacent side face of the corresponding gear to normally provide a pumping seal ftherewith, a relief recess formed in the gear engaging face of said end plate radially inwardly of its outer periphery to limit the sealing area between said end plate and said gear side face, a spring interposed between said housing and the outer terminal of said end plate effective to assure an initial pumping seal upon starting, means establishing communication between said relief recess and said inlet, means establishing restricted iiow communication between the discharge side of the corresponding gears and said pressure chamber at the back face of said end plate, the relation of the area of said back face to said sealing area being such that the force acting upon said back face of said end plate normally slightly exceeds the force acting on said front face whereby to maintain said pumping seal without excessive friction wear or loss in volumetric efficiency; control valve means in communication with the pressure acting in said pressure chamber for relieving the same to permit Vpumps whereby the generation of a combined koutput pressure of a selected predetermined maximum value becomes effective to operate said pilot valve relieving the loading pressure in said chamber, thus unloading said first pair of gears, said second pump continuing to deliver liquid pressure to said outlet and to said pilot control valve motive'surface effective to maintain said pilot control valve open and thus preventing said end plate from prematurely reengaging to reload said first pair of gears.

8. In a liquid pressure. powergenerating unit, means defining a first fixed displacement intermeshing gear type pump; means defining a second relatively small capacity fixed displacement intermeshing gear type pump; means connecting said pumps in continuous driving relation; said pumps having a common inlet and delivering to a common outlet; one-way check -valve means interposed between the discharge sides of the gears of said pump effective to permit flow from said first pump to said second pump but preventing flow from said second pump to said first pump; said first pump including an axially adjustable end plate engageable with the associated gear side face i for providing a pumping seal therewith and means for delivering pressure fluid generated by the corresponding gears into communication with the rear surface of said end plate for pressure loading said end plate; and means defining a pilot control valve assembly effective upon the generation of a common outlet pressure of predetermined selected value effective to relieve the loading pressure from communication with the rear surface of said end plate and thus unload said first pump said pilot control valve assembly including a valve proper, in communication with thepressure acting on said rear surface 'of said end plate, spring means normally urging said valve in the direction of its seat against the now from said back face, motive means connected with said valve effective when operated to open said valve and relieve said loading pressure, means placing said motive means in communication with ,y the combined output pressure from said pumps beyond said check valve, saidvalve and motive means including opposed balanced surfaces rendering said valve assembly nonresponsive to the pressure acting on the back face of said end plate. f

9. In a liquid pressure generating power unit,

` `means defining an enclosing housing containing a firstl intermeshing gear pump and a second intermeshing gear pump, said housing having a common inlet to said pumps and a common outlet therefrom, said pumps having means connecting the same in continuous driving relation, each of said pumps including axially adjustable end plates, defining pumping seals with the adjacent gear side faces, means placing the rear surfaces of said plates in communication with pressures generated by the respective pumps effective to pressure load said plates, a one-way check valve in said housing effective to permit flow from said first pump to said common outlet but preventing fiow from said second pump to said first pump, means defining a pilotcontrol valve assemsaid seat, means placing said motive piston in pressure communication with the combined discharge pressures from said first and second pumps beyond said check valve, whereby the generation of a combined output pressure of a selected maximum value becomes effective to move said pilot valve to open position and relieve the loading pressure from the back face of the end plate of said first pump, while said second pump continues to deliver pressure iiuid to said common outlet, said combined output of said first and second pump comprising a relative .large volume at a relatively low pressure, thus defining a first stage of operation, while said second pump functions following the operation of said pilot control valve, to deliver a relatively small volume of pressure fluid at a relatively high pressure, thus defining a second stage of operation.

l0. In a high pressure liquid power generating unit comprising .a housing having a low pressure liquid inlet, a high pressure liquid outlet, means defining a first relatively large displacement intermeshing gear ty-pe pump in said housing means defining a second relatively small displacement intermeshing gear type pump in said housing, means connecting said pumps in continuous driving relationship, each of said pumps comprising axially adjustable end plates, means directing the discharge pressure from the respective pumps to the back faces of said end plates for pressure loading the same; means defining a, pilot control valve arrangement in pressure communication with the backface of the end plate of the relatively large displacement pump, said pilot control valve having a motive piston means placing said motive piston in communication with the combined outlet pressures of said first and second pumps effective upon the occurrence of a combined output pressure of a selected predetermined maximum value to operate said valve and relieve the loading pressure from the back side of said end plate associated with said relatively large displacement pump, said second relatvely small displacement pump being eiiective to continue delivering pressure fiuid to said common outlet; said combined discharge of said first' and second pumps defining a first stage of operation at relatively low pressure large volume of delivery while the operation of said second pump following the unloading of said relatively large `pump being effective to define a second stage of operation at relatively high pressure small volume of' delivery.

11. In a 'liquid pressure power generating unit, means defining a first fixed displacement intermeshing gear type pump of the type employing pressure loaded bushings, means defining a second fixed displacement intermeshing gear type pump, a common inlet and a common outlet for said pumps, means interposed between the outlet sides of said first and second pumps effective to prevent fiow from the second pump to the first pump. and means responsive to the generation of a combined delivery pressure of a predetermined maximum value effective to cause lunloading of thepressure loaded bushings of said first pump while maintaining said second pump in operation.

12. A hydraulic power unit including a first 15 intermeshing gear type pump, pressure loadable bushings associated with the gears of said pump. said bushings being movable axially away from the associated gears to unload said pump. a second intermeshing gear type pump, a common inlet and a common outlet for said two pumps, and means responsive to the generation of a, combined delivery pressure of a predetermined maximum value effective to cause unloading of the rst pump -while maintaining said second pump in operation to deliver liquid pressure.

13. In a liquid pressure generating power unit, means defining an enclosing housing having a first pump chamber receiving a first pair of intermeshing gears, end plate bushing and bearing defining means normally received in pumping seal engagement with the side faces of said gears, said bushings each including a fiange radially outwardly coextensive with the adjacent gear teeth, the terminal surface of said ila-nge engaging with the adjacent gear side face in pumping seal rela-tion, said bushing means including a pressure responsive surface opposed to said terminal surface and spaced from theadjacent housing wall forming with said housing a motive pressure chamber, means defining a restricted flow passage for delivering liquid pressure generated by the corresponding gears to said pressure chamber for normally urging said bushing means into pumping seal engagement with the correspond ing gear side face; a second pump chamber in said housing receiving a second pair of intermeshing gears, said housing having a common inlet to said pairs of gears and a common outlet therefrom, a one-way check valve in said housing interposed between said pairs of gears effective to .prevent reverse ow from said second pair of gears to said first pair of gears; means dening a pilot control valve assembly effective upon the occurrence of a combined discharge pressure of a selected maximum value to relieve said pressure uid from said pressure chamber of said first pump and permit said bushing means to move axially out of sealing contact with the associated gears and hence unload said rst pair of gears, while said second pair of gears continue to deliver liquid pressure to said common outlet.

JOHN A. LAUCK.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,011,269 Sundh Dec. 13, 1911 1,532,326 Lendt et al Apr. 7, 1925 1,879,219 Harbison Sept. 2'7, 1932 2,420,622 Roth et al May 13, 1947 2,472,031 Wichorek May 31, 1949 

